The present invention relates to a radial set packer for sealing with a casing or other downhole cylindrical surface. More particularly, the present invention relates to a packer element which is configured with a primary seal and a backup seal, and may be part of a downhole tool including a conveyance tubular and a conical wedge ring. The packer element may be used for reliable sealing engagement between a liner hanger and a casing string.
Packer elements or packers which are radially set by axial movement of the packer element relative to a conical wedge ring have been used for sealing in subterranean well bores. A conveyance tubular is conventionally provided for positioning the packer element at the desired position within the well bore, and an actuator causes the packer element to move axially with respect to a conical wedge ring and thereby expand into sealing engagement with the cylindrical surface to be sealed.
U.S. Pat. Nos. 4,757,860 and 5,076,356 disclose radial set packer elements which may be used in various applications, including a subsea wellhead. In a typical wellhead application, the packer element may need to expand in diameter approximately 0.030 inches in order to obtain a reliable seal with the polished bore.
U.S. Pat. Nos. 5,511,620 and 5,333,692 disclose packer elements intended for sealing between a liner hanger and a casing. More specifically, a conical member is moved axially with respect to the packer element to expand the packer element into engagement with a casing. That expansion may be significantly greater than the expansion of a packer element in a wellhead application due to the difference in diameter of the casing from the drift ID (smallest allowable ID for a particular size casing) to the maximum ID allowed by API for that size casing. The difference between this drift ID and the maximum ID for a particular size casing may thus be 0.300 inches or greater.
Several problems exist with the packer element disclosed in the ""620 Patent. Because the seal element is stationary with respect to a movable conical element, the radially extending flanges or ribs of the seal element may not expand as desired into portions of the non-uniform diameter casing string to obtain reliable metal-to-metal sealing engagement. Also, the packer element does not always form a reliable metal-to-metal seal with the conical wedge ring, and the conical wedge ring similarly does not form a reliable metal-to-metal seal with the tool mandrel. Also, the elastomeric sealing portions of the seal element are not allowed to thermally expand in response to high temperature downhole conditions, and thus exert uncontrollable forces on the spaced apart metal radial flanges or ribs.
Other problems with prior art packer elements concern poor sealing reliability under high pressure conditions. The metal ribs may not reliably seal with the cylindrical surface, and the elastomeric portion of the seal assembly may not reliably seal over extended time periods. Some packer elements function reasonably well when high pressure is applied to one side of the packer element, but do not perform well when high fluid pressure is applied to the other side of the packer element.
The disadvantages of the prior art are overcome by the present invention, and an improved packer element and a tool including the improved packer element is hereinafter disclosed for reliably sealing between the packer mandrel and a downhole cylindrical surface.
The radial set annular packer element according to the present invention is positioned downhole by a conveyance tubular. The packer element may be moved by a setting tool from a reduced diameter run-in position to a set and expanded diameter position, such that the packer element engages a casing, a polished bore receptacle, or other downhole cylindrical surface in a well. If the cylindrical surface is a casing or other member which may be irregularly shaped, the packer element is preferably moved axially relative to a conical wedge ring or cone during the setting operation. The packer element is particularly well suited for reliably sealing against high pressure either from above or below the element, and includes a primary elastomeric seal and a secondary elastomeric seal, and a primary metallic seal and a secondary metallic seal. The metal ribs of the packer element are angled so that the primary elastomeric seal is pressed against a rib angled toward the high pressure, and the secondary elastomeric seal is similarly pressed against a rib angled toward the high pressure. The secondary elastomeric seal body acts on the primary rib to prevent the primary rib from becoming perpendicular with respect to the sealing surface, and thereby enhances the reliability of the seal.
It is an object of the present invention to provide an improved packer element which may be used in downhole applications for reliably sealing with a cylindrical surface. It is a feature of the present invention that the packer element is particularly well suited for sealing between a liner hanger and a casing under conditions where the casing may grow considerably in response to thermal and/or pressure expansion during downhole operations.
It is a related object of the invention to provide a downhole tool including a conveyance tubular, a conical wedge ring and an annular seal assembly or packer element according to the present invention.
It is a feature of the present invention that each of the primary and the backup metallic ribs of the sealing element are angled at least 15xc2x0 with respect to a plane perpendicular to a central axis of the sealing element.
Another feature of the invention is that axially spaced metal protrusions provide a reliable metal-to-metal seal between the packer element and the cone, and also preferably between the cone and the mandrel or body interior of the cone.
Still another feature of the invention is that the elastomeric seal bodies of the packer element include specifically designed volumetric voids so that, after the seal bodies engage the surface, the elastomeric seal bodies will be compressed until the ends of the ribs engage the sealing surface. At this stage, the now smaller voids in the seal bodies allow for thermal expansion of each seal body between the metal ribs to minimize undesirable stress force on the ribs.